Clinical chemistry of modern vintage is designed to undertake a maximum number of tests. These tests are conducted on hundreds of similar samples. It is often necessary in this testing, to aspirate fluid from open mouthed elongated receptacles containing these samples. In the case of aspirating liquid from a two phase liquid-solid system, such as centrifuged blood or other similarly treated biological specimens, it is important to prevent the removal of any of the solid phase from the receptacle, particularly where testing is to be conducted on the solid phase.